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Abstract:

The tips of gas turbine engine turbine rotor blades are provided with an
abrasive layer and the abrasive layer comprises chromised silicon carbide
grit protruding from a layer of material. In particular the abrasive
layer comprises a mixture of cubic boron nitride grit and chromised
silicon carbide grit and the cubic boron nitride grit and the chromised
silicon carbide grit protruding from the layer of material. The cubic
boron nitride grit has a greater dimension than the chromised silicon
carbide grit. The cubic boron nitride grit cuts the majority of a track
in an abradable structure and then the chromised silicon carbide grit
provides any additional cutting of the abradable structure.

2. A component as claimed in claim 1 wherein the cubic boron nitride grit
has a dimension of 100 to 150 micrometers and the chromised silicon
carbide grit has a dimension of 40 to 90 micrometers.

3. A component as claimed in claim 2 wherein the cubic boron nitride grit
has a dimension of 100 to 150 micrometers and the chromised silicon
carbide grit has a dimension of 50 to 80 micrometers.

4. A component as claimed in claim 1 wherein the layer of material further
comprises a metal.

5. A component as claimed in claim 1 wherein the component further
comprises a gas turbine engine component.

6. A component as claimed in claim 5 wherein the gas turbine engine
component is selected from the group comprising a compressor rotor blade
and a turbine rotor blade.

7. A method of applying an abrasive layer on a component comprising the
steps of:providing a mixture of cubic boron nitride grit,providing
chromised silicon carbide grit to create a mixture,wherein the cubic
boron nitride grit has a greater dimension than the chromised silicon
carbide grit, andsecuring the mixture of cubic boron nitride grit and
chromised silicon carbide grit to the component using a layer of
material.

8. A method as claimed in claim 7 wherein the mixture of cubic boron
nitride grit and chromised silicon carbide grit is secured to the
component by the step of brazing the layer of material onto the
component.

9. A method as claimed in claim 7 wherein the mixture of cubic boron
nitride grit and chromised silicon carbide grit is secure to the
component by the step of electroplating the layer of material onto the
component.

10. A method as claimed in claim 7 wherein the mixture of cubic boron
nitride grit and chromised silicon carbide grit is secured to the
component by the step of direct laser deposition of the layer of material
onto the component.

11. A method as claimed in claim 7 wherein the mixture of cubic boron
nitride grit and chromised silicon carbide grist is secured to the
component by the step of melting the component by direct laser deposition
to form the layer of material.

12. A method as claimed in claim 7 wherein the cubic boron nitride grit
has a dimension of 100 to 150 micrometers and the chromised silicon
carbide grit has a dimension of 40 to 90 micrometers.

13. A method as claimed in claim 12 wherein the cubic boron nitride grit
has a dimension of 100 to 150 micrometers and the chromised silicon
carbide grit has a dimension of 50 to 80 micrometers.

14. A method as claimed in claim 7 wherein the layer of material comprises
a metal.

15. A method as claimed in any claim 7 wherein the component is a gas
turbine engine component.

16. A method as claimed in claim 15 wherein the gas turbine engine
component is selected from the group comprising a compressor rotor blade
and a turbine rotor blade.

17. A component having an abrasive layer, wherein the abrasive layer
comprises chromised silicon carbide grit protruding from a layer of
material.

18. A method of applying an abrasive layer on a component, comprising
providing chromised silicon carbide grit and securing the chromised
silicon carbide grit to the component using a layer of material.

Description:

CROSS REFERENCE TO RELATED APPLICATION

[0001]This application is entitled to the benefit of British Patent
Application No. GB 0822703.5, filed on Dec. 15, 2008.

FIELD OF THE INVENTION

[0002]The present invention relates to a component having an abrasive
layer and in particular to a gas turbine engine turbine rotor blade
having an abrasive layer or a gas turbine engine compressor rotor blade
having an abrasive layer.

BACKGROUND OF THE INVENTION

[0003]Cubic boron nitride grit is used in an abrasive layer on the tips of
gas turbine engine turbine rotor blades and/or compressor rotor blades to
cut a track in an abradable material on a surrounding casing to form a
seal between the tips of the rotor blades and the casing.

[0004]Cubic boron nitride suffers from high temperature oxidation, e.g.
cubic boron nitride has a relatively short oxidation life, about 25
hours, at the operating temperature of a turbine of a gas turbine engine.
This reduces the cutting performance of the cubic boron nitride grit at
later stages in the operational life of the turbine of a gas turbine
engine. However, cubic boron nitride grit is still of interest for use in
the turbine of a gas turbine engine because cubic boron nitride is able
to cut into ceramic abradable material and the majority of the cutting of
the track in the abradable material occurs during initial running-in of
the gas turbine engine.

[0007]However, the aluminium nitride is eroded from the cubic boron
nitride grit in use and then the cubic boron nitride grit is oxidised.

[0008]Silicon carbide grit does not suffer from high temperature
oxidation. However, the shear strength and hardness of silicon carbide
grit are less than cubic boron nitride grit but silicon carbide grit is
able to cut into ceramic abradable material. In addition silicon carbide
grit is susceptible to diffusion into the turbine blade nickel based
superalloys and produces deleterious silicides in the nickel based
superalloy.

[0009]Our published UK patent application GB2301110A discloses an abrasive
layer for a turbine blade that includes silicon carbide grit coated with
aluminium nitride. The aluminium nitride reduces, or prevents, diffusion
of the silicon carbide into the nickel based superalloy of the turbine
blade.

[0010]Alumina grit is not hard enough to cut into ceramic abradable
material.

SUMMARY OF THE INVENTION

[0011]Accordingly, the present invention seeks to provide a component
having a novel abrasive layer which reduces, Preferably, overcomes, the
above mentioned problem.

[0012]Accordingly, the present invention provides a component having an
abrasive layer, wherein the abrasive layer comprises a mixture of cubic
boron nitride grit and chromised silicon carbide grit, the cubic boron
nitride grit and the chromised silicon carbide grit protruding from the
layer of material, the cubic boron nitride grit having a greater
dimension than the chromised silicon carbide grit.

[0013]Preferably, the cubic boron nitride grit has a dimension of 100 to
150 micrometers and the chromised silicon carbide grit has a dimension of
40 to 90 micrometers.

[0014]Preferably, the cubic boron nitride grit has a dimension of 100 to
150 micrometers and the chromised silicon carbide grit has a dimension of
50 to 80 micrometers.

[0015]Preferably, the layer of material includes a metal.

[0016]Preferably, the component includes a gas turbine engine component.

[0017]Preferably, the gas turbine engine component includes a compressor
rotor blade or a turbine rotor blade.

[0018]The present invention also provides a method of applying an abrasive
layer on a component, having the steps of providing a mixture of cubic
boron nitride grit and chromised silicon carbide grit, the cubic boron
nitride grit having a greater dimension than the chromised silicon
carbide grit and securing the mixture of cubic boron nitride grit and
chromised silicon carbide grit to the component using the layer of
material.

[0019]Preferably, the mixture of cubic boron nitride grit and chromised
silicon carbide grit is secured to the component by brazing, or
electroplating, the layer of material onto the component.

[0020]Alternatively, the mixture of cubic boron nitride grit and chromised
silicon carbide grit is secured to the component by direct laser
deposition of the layer of material onto the component or by melting the
component by direct laser deposition to form the layer of material.

[0021]Preferably, the cubic boron nitride grit has a dimension of 100 to
150 micrometers and the chromised silicon carbide grit has a dimension of
40 to 90 micrometers.

[0022]Preferably, the cubic boron nitride grit has a dimension of 100 to
150 micrometers and the chromised silicon carbide grit has a dimension of
50 to 80 micrometers.

[0026]The present invention also provides a component having an abrasive
layer, wherein the abrasive layer comprises chromised silicon carbide
grit protruding from a layer of material.

[0027]The present invention also provides a method of applying an abrasive
layer on a component, comprising providing chromised silicon carbide grit
and securing the chromised silicon carbide grit to the component using a
layer of material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 shows a turbofan gas turbine engine having a component having
an abrasive layer according to the present invention.

[0029]FIG. 2 is an enlarged view of a component having an abrasive layer
according to the according to the present invention.

[0030]FIG. 3 is a further enlarged view of an abrasive layer according to
the present invention in a manufactured condition.

[0031]FIG. 4 is a further enlarged view of an abrasive layer according to
the present invention in a used condition.

[0033]The high-pressure turbine 23 of the turbine section 20 is shown more
clearly in FIG. 2. The high-pressure turbine 23 comprises one or more
stages of turbine rotor blades 26 arranged alternately with one or more
stages of stator vanes 30. Each of the turbine rotor blades 26 comprises
a root 34, a shank 35, a platform 36 and an aerofoil 38. The turbine
rotor blades 26 are arranged circumferentially around a turbine rotor 24
and the turbine rotor blades 26 extend generally radially from the
turbine rotor 24. The roots 34 of the turbine rotor blades 26 are located
in axially extending slots 25 in the periphery of the turbine rotor 24.
The platforms 36 of the turbine rotor blades 26 together define the inner
boundary of a portion of the flow path through the high-pressure turbine
23. The aerofoils 38 of the turbine rotor blades 26 have leading edges
40, trailing edges 42 and tips 44 at their radially outer extremities.

[0034]Alternatively, the turbine rotor blades 26 are integral with the
turbine rotor 24 and are friction welded, electron beam welded or laser
beam welded to the turbine rotor 24.

[0035]The turbine stator vanes 30 also comprise aerofoils 52, which have
platforms 56 at their radially inner ends and shrouds 54 at their
radially outer ends. The turbine stator vanes 30 are also arranged
circumferentially around the stator and extend generally radially. The
shrouds 54 of the turbine stator vanes 30 are secured together to form a
stator casing 28. A further outer stator casing 32 surrounds the stator
casing 28.

[0036]A small gap, or clearance, 45 is provided radially between the tips
44 of the turbine rotor blades 26 and the turbine casing 28. The turbine
casing 28 is provided with a seal 48, an abradable structure, on its
radially inner surface immediately around the tips 44 of the turbine
rotor blades 26.

[0037]These seals 48 are provided around each of the stages of the turbine
rotor blades 26, between the tips 44 of the turbine rotor blades 26 and
the stator casing 28. The seals 48 are carried on the shrouds 54 of the
stator vanes 30. The seals 48 comprise an abradable structure 59 on the
shrouds 54 of the stator vanes 30 of the turbine casing 28. The seals 48
comprise a ceramic material, for example zirconia or stabilised zirconia.

[0039]In particular, the cubic boron nitride grit 68 has a dimension of
100 to 150 micrometers and the chromised 64 silicon carbide grit 62 has a
dimension of 40 to 90 micrometers. In a particular example the cubic
boron nitride grit 68 has a dimension of 100 to 150 micrometers and the
chromised 64 silicon carbide grit 62 has a dimension of 50 to 80
micrometers.

[0040]The layer of material 66 comprises a layer of metal, for example the
layer of metal comprises a MCrAlY, where M is one or more of nickel,
cobalt and iron, Cr is chromium, Al is aluminium and Y is yttrium.

[0041]The chromised 64 silicon carbide grit 62 comprises silicon carbide
grit 62 in which chromium has been diffused into the outer layer of the
silicon carbide grit 62. The diffusion of chromium into the outer layer
of the silicon carbide grit 62 changes the composition of the outer layer
of the silicon carbide grit 62 to form a new alloy. The chromium is
diffused into the outer layer of the silicon carbide grit 62 using any
suitable process, for example pack chromising or vapour chromising.

[0042]The mixture of cubic boron nitride grit 68 and chromised 64 silicon
carbide grit 62 is secured to the tips 44 of the turbine rotor blades 26
by brazing or electroplating the layer of material 66 onto the tips 44 of
the turbine rotor blades 26.

[0043]Alternatively, the mixture of cubic boron nitride grit 68 and
chromised 64 silicon carbide grit 62 is secured to the tips 44 of the
turbine rotor blades 26 by direct laser deposition of the layer of
material 66 onto the tips 44 of the turbine rotor blades 26 or by melting
the tips 44 of the turbine rotor blades 26 by direct laser deposition to
form the layer of material 66.

[0044]As manufactured the cubic boron nitride grit 68 protrudes by a
greater distance from the outer surface of the layer of material 68 than
the chromised 64 silicon carbide grit 62, as shown in FIG. 3. In
operation of the gas turbine engine 10, the cubic boron nitride grit 68
cuts the majority of the track, the cubic boron nitride grit 68 cuts
about 90% of the depth of the track, in the abradable structure 59 on the
shrouds 54 during the initial running-in in the first 25 hours of
operation of the gas turbine engine. During service of the gas turbine
engine 10 the cubic boron nitride grit 68 is progressively oxidised
leaving only the chromised 64 silicon carbide grit 62, as shown in FIG.
4. The chromisied silicon carbide grit 62 then provides any additional
cutting of the abradable structure 59.

[0045]Although the present invention has been described with reference to
providing the abrasive layer on the tips of gas turbine engine turbine
rotor blades, it is equally possible to apply the abrasive layer to the
tips of gas turbine engine compressor rotor blades or other gas turbine
engine components where it is necessary to cut a track in an abradable
material on a cooperating component, e.g., sealing fins on a rotor and
abradable structure on a stator vane platform, labyrinth seals. The
present invention is applicable to axial and centrifugal flow
compressors, axial and radial flow turbines, turbochargers and power
turbines.